Re: [PATCH 1/2] sched/fair: Prefer fully-idle SMT cores in asym-capacity idle selection

Andrea Righi
2026-04-21T12:33:24Z

On Tue, Apr 21, 2026 at 02:26:58PM +0200, Vincent Guittot wrote:
...
> > > > Yeah, makes sense. I'm wondering if we should attach the shared blob to
> > > > sd_asym_cpucapacity only when asym is a non-overlapping domain, otherwise
> > > > fallback to sd_llc and, in this case, ignore has_idle_cores in
> > > > select_idle_capacity(). This might be not the best in terms of efficiency on
> > > > those exotic topologies, but it'd eliminate the overlap/aliasing risk, while
> > > > still being correct. What do you think?
> > >
> > > I slightly changed your patch adding this logic on top, I'll send an updated
> > > patch series, so it's easier to review/comment.
> >
> > Actually... while preparing the series I realized that in select_idle_capacity()
> > we may end up clearing the has_idle_cores hint even when the failure is due to
> > affinity constraints (no fit CPU in the allowed cpumask), not only when no fully
> > idle core is found in the system and this can lead to false has_idle_cores
> > hints.
>
> How is it different from select_idle_cpu() which does the same afaict ?

Nah, it was just me not reading the code right. It's the same with
select_idle_cpu(), so I'm back at using Prateek's patch.

Thanks,
-Andrea